Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
A light emitting device such as an LED is often combined with a wavelength converting material such as a phosphor. The use of a blue-emitting phosphor is known. For example, U.S. Pat. No. 7,938,983 teaches dichromatic and polychromatic white-emitting phosphor-converted LEDs. “A white-light emitting illumination system according to the invention can advantageously be produced by choosing the fluorescent material such that a UV radiation emitted by the UV light emitting diode is converted into complementary wavelength ranges, to form dichromatic white light. In this case, the amber and blue light is produced by means of the fluorescent materials . . . Blue light is produced by means of the fluorescent materials that comprise a blue phosphor selected from the group comprising BaMgAl10O17:Eux Ba5SiO4(Cl,Br)6Eu, CaLa2S4:Ce, (Sr,Ba,Ca)5(PO4)3Cl:Eu and LaSi3N5:Ce.”
“In a further embodiment, a white-light emitting illumination system according to the invention can advantageously be produced by choosing the fluorescent material such that UV radiation emitted by a UV emitting diode is converted into complementary wavelength ranges, to form polychromatic white light e.g. by additive color triads, for example blue, green and red.”
WO 2012033122 teaches “A blue-light-emitting phosphor which has a basic compositional formula Sr3-xMgSi2O8:Eux (wherein x represents a numeral value falling within the range from 0.008 to 0.110), has the same crystalline structure as that of merwinite, and has a crystal lattice strain of 0.080% or less as determined by a Le Bail method from an X-ray diffraction pattern at diffraction angle 2θ of 20-130°, wherein the X-ray diffraction pattern is determined using a CuKα ray having an incident angle of θ. The blue-light-emitting phosphor can be used advantageously as a blue-light-emitting material for a light-emitting device which comprises a semiconductor light-emitting element that can emit light having a wavelength of 350-430 nm upon the conduction of an electrical current, such as a white LED lamp, and a blue-light-emitting material that can emit blue light upon the excitation with light emitted by the semiconductor light-emitting element.”